The present invention relates to a process allowing the preparation of a (dialkylphosphono)alkyl (meth)acrylate, in particular of (dimethylphosphono)ethyl methacrylate.
American Patent U.S. Pat. No. 3,030,347 relates to copolymers based on dialkylphosphonoalkyl (meth)acrylate and a monomer which can be copolymerized with this compound. The dialkylphosphonoalkyl (meth)acrylate is prepared by addition of an alkyl phosphite C to an aldehyde, followed by reaction with (meth)acroyl chloride.
This latter reagent has the disadvantage of not being available on the industial scale and of generating significant amounts of effluents during its use.
There is therefore presently no process allowing (dialkylphosphono)alkyl (meth)acrylates to be prepared in a satisfactory manner on the industrial scale with a view, especially, to using them in industrial polymerization processes.
An object of the present invention is therefore a process for the preparation of (dialkylphosphono)alkyl (meth)acrylate which can easily be employed on the industrial scale.
More precisely, a first object of the present invention is a process for the preparation of a (dialkylphosphono)alkyl (meth)acrylate corresponding to the formula: 
in which:
R is a hydrogen or a methyl group
R1 is an alkyl group having from 1 to 6 carbon atoms, especially 1 or 2 carbon atoms;
n is an integer from 1 to 3.
This process comprises the reaction of an alkyl (meth)acrylate A of formula 
in which:
R is a hydrogen atom or a methyl group;
Rxe2x80x2 is an alkyl group having from 1 to 4 carbon atoms with a dialkylphosphonated alcohol B of formula: 
in which R1 and n have the meanings given above.
Such a process therefore has the advantage of resorting to a transesterification, which avoids requiring products which are not very available in the trade or with high toxicity. In addition, it allows (dialkylphosphono)alkyl (meth)acrylates to be prepared at low cost.
A second object of the present invention is a polymerization process in which the phosphonated monomer obtained by the preparation process according to the invention is polymerized with at least one C1 to C4 alkyl (meth)acrylate.
According to a preferred embodiment of the polymerization process of the invention, the phosphonated monomer is employed during the polymerization in the form of a solution of this monomer in the alkyl (meth)acrylate A which has served for its preparation.
Other characteristics and advantages of the invention will now be described in detail in the account which follows, and illustrated by the appended figure which represents the apparatus used for carrying out the process according to the invention.
Preparation of the (Dialkylphosphono)Alkyl (Meth)Acrylate
1) Reagents
Alkyl (meth)acrylate A
According to the invention, the starting material used is an alkyl (meth)acrylate A of formula: 
in which:
R is a hydrogen atom or a methyl group;
Rxe2x80x2 is an alkyl group having from 1 to 4 carbon atoms.
Preferably, the group R is the methyl group and the group Rxe2x80x2 is the methyl or ethyl, especially methyl, group.
As alkyl (meth)acrylate A, mention can therefore be made of methyl, ethyl, propyl, butyl acrylates and methyl, ethyl, propyl and butyl methacrylates.
The alkyl (meth)acrylate A is therefore reacted with the dialkylphosphonated alcohol B.
Dialkylphosphonated alcohol B
This compound has the formula: 
in which
R1 is an alkyl group having from 1 to 6 carbon atoms; and
n is an integer from 1 to 3.
Preferably, R1 contains 1 to 3 carbon atoms. More preferentially, R1 is a methyl or ethyl group.
To obtain a dialkylphosphonated alcohol B in which n is 2 or 3, a free-radical reaction is carried out, in a conventional manner, between an alkyl phosphite C of formula: 
in which R1 has the meaning given above,
and an unsaturated ester D of formula 
in which
R2 is an alkyl group containing from 1 to 4 carbon atoms, preferably a methyl,
nxe2x80x2 is 0 or 1;
then the intermediate E obtained, of formula: 
in which:
R1, R2 have the meanings indicated above
n is 2 or 3;
is saponified to result in the dialkylphosphonated alcohol B.
To obtain a dialkylphosphonated alcohol B in which n is 1, an alkyl phosphite C is reacted in a conventional manner with formaldehyde.
2) Reaction of the Alkyl (Meth)Acrylate A with the Dialkylphosphonated Alcohol B
This reaction is a transesterification reaction. It is therefore carried out under the conditions customary for transesterification reactions, which are well known to the person skilled in the art.
The temperatures employed are in general from 85xc2x0 C. to 130xc2x0 C., preferably from 95xc2x0 C. to 120xc2x0 C.
The ratio of the reagents, namely (meth)acrylic ester A: phosphonated alcohol B varies within large limits, for example between 1.4 and 5, preferably between 2 and 4.
Preferably, the reaction is carried out in the presence of a catalyst, in a quantity of between 10xe2x88x924 and 10xe2x88x921, preferably between 5.10xe2x88x924 and 5.10xe2x88x922, mol/mol of alcohol.
As catalyst, zirconium acetylacetonate is preferentially used.
(Dialkylphosphono)Alkyl (Meth)Acrylate Monomer
The final product, namely the (dialkylphosphono)alkyl (meth)acrylate monomer, can serve for the preparation of textile binders having a nonflammable character.
Its insensitivity to hydrolysis can also be turned to good account by producing aqueous dispersions useful as paint binders for metals.
It can also be used in order to prepare polymers of low mass which can be employed as dispersants for fillers.
It finds particularly interesting applications in the manufacture of latexes, because it confers to the latter properties of adhesion to metals or anti-corrosion properties, although the anti-corrosion properties are normally obtained by means of chromium atoms.